Find Axle Ratio
There are a few different methods you can use to determine the ratio of your axle, depending on what model of axle you have. These ideas should help you in determining the ratio of your axle:
The most sure way to determine your ratio is to count the number of teeth on the ring gear and divide it by the number of teeth on the pinion. For example, if you count 41 teeth on the ring gear and 9 teeth on the pinion, you would divide 41 by 9=4.56. Your ratio would be 4.56:1. That means that for every time your axle shaft makes one complete rotation, your driveline will turn 4.56 complete revolutions.
Another method that can be used on a Dana axle, and in most cases will work on other axles, is to get all of the numbers off of the edge of the ring gear. If you forward those numbers to me, I can look them up and determine what ratio you have.
Also on a Dana axle, if you can find a bill of material number and forward it to me, I can look it up and it will tell me what ratio you have, assuming that there have not been any modifications made to your axle since it was manufactured.
In some cases, there is a metal tag bolted on somewhere around the differential cover. This tag should have the ratio stamped on it.
If none of these methods work for you, don’t give up hope. You can always call your local Ford, GM, Jeep, or Chrysler dealer with your vehicle’s VIN number, and they should be able to tell you what ratio you have. Again, this is assuming that there have not been any modifications made to your axle since it was manufactured.
Attention 4WD Owners:
If by chance you have a 4WD vehicle, and cannot find any information on one of your axles, check the other, as it will be the same ratio. Remember, this only applies to a 4WD vehicle.
For example, I have had many cases where someone has blown up their rear end to the point where they could not count the number of teeth on the ring gear or pinion, or find any numbers on the ring gear to determine the ratio. We were able to check the front axle and determine the ratio that way. This is why ratio is very important in a 4WD vehicle.
I have had people swap out their rear end and not match the ratio in the front with the ratio in the rear. They drive their vehicle in two wheel drive without any problems, until they shift into 4WD. When they engage the 4WD and try to drive the vehicle, all heck breaks loose! Because the front axle is turning at a different speed than the rear, something has to give. It can be almost anything, transfer case, driveline, ring & pinion, or axle shaft. Something will break!